The subject matter disclosed herein relates to a system for transferring thermal energy, and in particular to a heat exchanger system that can de-congeal oil within a heat exchanger at low operating temperatures.
Heat exchangers are used in a variety of applications to remove or transfer thermal energy from a first area, such as a gas turbine engine for example, to a second area, such as an air stream for example. In the case of a gas turbine engine, a heat transfer medium such as oil is circulated into a heat exchanger. The heat exchanger has a plurality of fins that extend into an air stream. The fins are thermally coupled to a plurality of small channels through which the oil flows. The thermal energy is transferred from the oil into the fins causing a reduction in the temperature of the oil. Air moving over the fins causes a transfer of thermal energy into the air stream that removes it from the system.
One issue that arises with an oil-air heat exchanger occurs during low operating temperatures. In some applications, the operating temperatures may drop below −40 C to −54 C. In these environments, the oil may congeal and the oil viscosity increases such that the pressure required to drive the flow through the heat exchanger may damage the fins. Thermal bypass valves are provided to allow the oil to flow around the heat exchanger under these conditions. The bypass operation continues until the temperature of the oil reaches a desired temperature. However, since the heat exchanger is bypassed, the oil within the heat exchanger may still at a temperature too low for flowing oil through the heat exchanger.
In other applications, multiple heat exchangers are arranged in parallel. Each of the heat exchangers has its own bypass valve that allows the oil to be warmed under cold operating conditions. Similar to the situation with a single heat exchanger, the bypassing of the oil allows a reduction in the viscosity of the bypassed oil, but oil within the heat exchangers will remain congealed. Another issue that arises with multiple heat exchangers is when an issue arises with one of the bypass valves, such as being stuck in a bypass configuration. When this occurs, a less than desired amount of thermal energy may be transferred causing higher operating temperatures. Since each of the heat exchangers is arranged in parallel, the operator may not be able to quickly identify which of the bypass valves is not operating as desired.
Accordingly, while existing oil-air heat exchangers are suitable for their intended purposes there remains a need for improvements, particularly regarding the de-congealing of oil within the heat exchanger and in reducing the number of components within the system.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.